LabelCheckbox no longer expands vertically

It should in theory valign to middle this way, but grid layout
suffers from #1

README.md

@@ -1,4 +1,6 @@
 # objects
 
+[![Go Reference](https://pkg.go.dev/badge/git.tebibyte.media/tomo/objects.svg)](https://pkg.go.dev/git.tebibyte.media/tomo/objects)
+
 Objects contains a standard collection of re-usable objects. All objects in this
 module visually conform to whatever the theme is set to.

button.go

@@ -4,10 +4,20 @@ import "git.tebibyte.media/tomo/tomo"
 import "git.tebibyte.media/tomo/tomo/theme"
 import "git.tebibyte.media/tomo/tomo/input"
 import "git.tebibyte.media/tomo/tomo/event"
+import "git.tebibyte.media/tomo/objects/layouts"
+
+var buttonLayout     = layouts.NewGrid([]bool { true        }, []bool { true })
+var iconButtonLayout = layouts.NewGrid([]bool { false       }, []bool { true })
+var bothButtonLayout = layouts.NewGrid([]bool { false, true }, []bool { true })
 
 // Button is a clickable button.
 type Button struct {
-	tomo.TextBox
+	tomo.ContainerBox
+
+	label *Label
+	icon  *Icon
+	labelActive bool
+	
 	on struct {
 		click event.FuncBroadcaster
 	}
@@ -15,21 +25,71 @@ type Button struct {
 
 // NewButton creates a new button with the specified text.
 func NewButton (text string) *Button {
-	box := &Button { TextBox: tomo.NewTextBox() }
+	box := &Button {
+		ContainerBox: tomo.NewContainerBox(),
+		label:        NewLabel(text),
+	}
 	theme.Apply(box, theme.R("objects", "Button", ""))
+	box.label.SetAlign(tomo.AlignMiddle, tomo.AlignMiddle)
+	box.SetLayout(buttonLayout)
 	box.SetText(text)
-	box.SetAlign(tomo.AlignMiddle, tomo.AlignMiddle)
+	
+	box.CaptureDND(true)
+	box.CaptureMouse(true)
+	box.CaptureScroll(true)
+	box.CaptureKeyboard(true)
+	
 	box.OnMouseUp(box.handleMouseUp)
 	box.OnKeyUp(box.handleKeyUp)
 	box.SetFocusable(true)
 	return box
 }
 
+// SetText sets the text of the button's label.
+func (this *Button) SetText (text string) {
+	this.label.SetText(text)
+	if this.labelActive && text == "" {
+		this.Delete(this.label)
+		this.labelActive = false
+	}
+	if !this.labelActive && text != "" {
+		this.Add(this.label)
+		this.labelActive = true
+	}
+	this.applyLayout()
+}
+
+// SetIcon sets an icon for this button. Setting the icon to IconUnknown will
+// remove it.
+func (this *Button) SetIcon (id theme.Icon) {
+	if this.icon != nil { this.Delete(this.icon) }
+
+	var icon *Icon; if id != theme.IconUnknown {
+		icon = NewIcon(id, theme.IconSizeSmall)
+	}
+	this.icon = icon
+
+	if this.icon != nil {
+		this.Insert(this.icon, this.label)
+	}
+	this.applyLayout()
+}
+
 // OnClick specifies a function to be called when the button is clicked.
 func (this *Button) OnClick (callback func ()) event.Cookie {
 	return this.on.click.Connect(callback)
 }
 
+func (this *Button) applyLayout () {
+	if this.labelActive && this.icon == nil {
+		this.SetLayout(buttonLayout)
+	} else if !this.labelActive && this.icon != nil {
+		this.SetLayout(iconButtonLayout)
+	} else {
+		this.SetLayout(bothButtonLayout)
+	}
+}
+
 func (this *Button) handleKeyUp (key input.Key, numberPad bool) {
 	if key != input.KeyEnter && key != input.Key(' ') { return }
 	this.on.click.Broadcast()

checkbox.go

@@ -0,0 +1,69 @@
+package objects
+
+import "git.tebibyte.media/tomo/tomo"
+import "git.tebibyte.media/tomo/tomo/theme"
+import "git.tebibyte.media/tomo/tomo/input"
+import "git.tebibyte.media/tomo/tomo/event"
+
+// Checkbox is a control that can be toggled.
+type Checkbox struct {
+	tomo.Box
+	value bool
+	on struct {
+		valueChange event.FuncBroadcaster
+	}
+}
+
+// NewCheckbox creates a new checkbox with the specified value.
+func NewCheckbox (value bool) *Checkbox {
+	box := &Checkbox {
+		Box: tomo.NewBox(),
+	}
+	theme.Apply(box, theme.R("objects", "Checkbox", ""))
+	box.SetValue(false)
+	
+	box.OnMouseUp(box.handleMouseUp)
+	box.OnKeyUp(box.handleKeyUp)
+	box.SetFocusable(true)
+	return box
+}
+
+// SetValue sets the value of the checkbox.
+func (this *Checkbox) SetValue (value bool) {
+	this.value = value
+	if this.value {
+		// TODO perhaps have IconStatusOkay/Cancel in actions, and have
+		// a status icon for checked checkboxes.
+		this.SetTexture(theme.IconStatusOkay.Texture(theme.IconSizeSmall))
+	} else {
+		this.SetTexture(nil)
+	}
+}
+
+// Toggle toggles the value of the checkbox between true and false.
+func (this *Checkbox) Toggle () {
+	this.SetValue(!this.Value())
+}
+
+// Value returns the value of the checkbox.
+func (this *Checkbox) Value () bool {
+	return this.value
+}
+
+// OnValueChange specifies a function to be called when the checkbox's value
+// changes.
+func (this *Checkbox) OnValueChange (callback func ()) event.Cookie {
+	return this.on.valueChange.Connect(callback)
+}
+
+func (this *Checkbox) handleKeyUp (key input.Key, numberPad bool) {
+	if key != input.KeyEnter && key != input.Key(' ') { return }
+	this.Toggle()
+}
+
+func (this *Checkbox) handleMouseUp (button input.Button) {
+	if button != input.ButtonLeft { return }
+	if this.MousePosition().In(this.Bounds()) {
+		this.Toggle()
+	}
+}

container.go

@@ -23,13 +23,23 @@ func newContainer (layout tomo.Layout, children ...tomo.Object) *Container {
 	return this
 }
 
-// NewOuterContainer creates a new container that has padding around it.
+// NewOuterContainer creates a new container that has padding around it, as well
+// as a solid background color. It is meant to be used as a root container for a
+// window, tab pane, etc.
 func NewOuterContainer (layout tomo.Layout, children ...tomo.Object) *Container {
 	this := newContainer(layout, children...)
 	theme.Apply(this, theme.R("objects", "Container", "outer"))
 	return this
 }
 
+// NewSunkenContainer creates a new container with a sunken style and padding
+// around it. It is meant to be used as a root container for a ScrollContainer.
+func NewSunkenContainer (layout tomo.Layout, children ...tomo.Object) *Container {
+	this := newContainer(layout, children...)
+	theme.Apply(this, theme.R("objects", "Container", "sunken"))
+	return this
+}
+
 // NewInnerContainer creates a new container that has no padding around it.
 func NewInnerContainer (layout tomo.Layout, children ...tomo.Object) *Container {
 	this := newContainer(layout, children...)

dialog.go

@@ -0,0 +1,101 @@
+package objects
+
+import "image"
+import "git.tebibyte.media/tomo/tomo"
+import "git.tebibyte.media/tomo/tomo/event"
+import "git.tebibyte.media/tomo/tomo/theme"
+import "git.tebibyte.media/tomo/objects/layouts"
+
+// DialogKind defines the semantic role of a dialog window.
+type DialogKind int; const (
+	DialogInformation DialogKind = iota
+	DialogQuestion
+	DialogWarning
+	DialogError
+)
+
+// Dialog is a modal dialog window.
+type Dialog struct {
+	tomo.Window
+	controlRow tomo.ContainerBox
+}
+
+type clickable interface {
+	OnClick (func ()) event.Cookie
+}
+
+// NewDialog creates a new dialog window given a dialog kind.
+func NewDialog (kind DialogKind, parent tomo.Window, title, message string, options ...tomo.Object) (*Dialog, error) {
+	if title == "" {
+		switch kind {
+		case DialogInformation: title = "Information"
+		case DialogQuestion:    title = "Question"
+		case DialogWarning:     title = "Warning"
+		case DialogError:       title = "Error"
+		}
+	}
+
+	dialog := &Dialog { }
+	if parent == nil {
+		window, err := tomo.NewWindow(image.Rectangle { })
+		if err != nil { return nil, err }
+		dialog.Window = window
+	} else {
+		window, err := parent.NewModal(image.Rectangle { })
+		if err != nil { return nil, err }
+		dialog.Window = window
+	}
+
+	var iconId theme.Icon
+	switch kind {
+	case DialogInformation: iconId = theme.IconStatusInformation
+	case DialogQuestion:    iconId = theme.IconStatusQuestion
+	case DialogWarning:     iconId = theme.IconStatusWarning
+	case DialogError:       iconId = theme.IconStatusError
+	}
+	dialog.SetTitle(title)
+	icon := NewIcon(iconId, theme.IconSizeLarge)
+	messageText := NewLabel(message)
+	messageText.SetAlign(tomo.AlignStart, tomo.AlignMiddle)
+
+	for _, option := range options {
+		if option, ok := option.(clickable); ok {
+			option.OnClick(dialog.Close)
+		}
+	}
+	dialog.controlRow = NewInnerContainer(layouts.ContractHorizontal, options...)
+	dialog.controlRow.SetAlign(tomo.AlignEnd, tomo.AlignEnd)
+
+	dialog.SetRoot(NewOuterContainer (
+		layouts.NewGrid([]bool { true }, []bool { true, false }),
+		NewInnerContainer(layouts.ContractHorizontal, icon, messageText),
+		dialog.controlRow))
+	return dialog, nil
+}
+
+// NewDialogOk creates a new dialog window with an OK option.
+func NewDialogOk (kind DialogKind, parent tomo.Window, title, message string, onOk func ()) (*Dialog, error) {
+	okButton := NewButton("OK")
+	okButton.SetIcon(theme.IconStatusOkay)
+	okButton.OnClick(func () {
+		if onOk != nil { onOk() }
+	})
+	okButton.SetFocused(true)
+	
+	return NewDialog(kind, parent, title, message, okButton)
+}
+
+// NewDialogOkCancel creates a new dialog window with OK and Cancel options.
+func NewDialogOkCancel (kind DialogKind, parent tomo.Window, title, message string, onOk func ()) (*Dialog, error) {
+	cancelButton := NewButton("Cancel")
+	cancelButton.SetIcon(theme.IconStatusCancel)
+	
+	okButton := NewButton("OK")
+	okButton.SetIcon(theme.IconStatusOkay)
+	okButton.OnClick(func () {
+		if onOk != nil { onOk() }
+	})
+	okButton.SetFocused(true)
+
+	return NewDialog(kind, parent, title, message, cancelButton, okButton)
+}

go.mod

@@ -2,6 +2,6 @@ module git.tebibyte.media/tomo/objects
 
 go 1.20
 
-require git.tebibyte.media/tomo/tomo v0.23.0
+require git.tebibyte.media/tomo/tomo v0.31.0
 
 require golang.org/x/image v0.11.0 // indirect

go.sum

@@ -1,5 +1,5 @@
-git.tebibyte.media/tomo/tomo v0.23.0 h1:OZwI4oLKMP7JqFc98VxBoRxwjL+W9NyTQZLB/m1BvaA=
-git.tebibyte.media/tomo/tomo v0.23.0/go.mod h1:C9EzepS9wjkTJjnZaPBh22YvVPyA4hbBAJVU20Rdmps=
+git.tebibyte.media/tomo/tomo v0.31.0 h1:LHPpj3AWycochnC8F441aaRNS6Tq6w6WnBrp/LGjyhM=
+git.tebibyte.media/tomo/tomo v0.31.0/go.mod h1:C9EzepS9wjkTJjnZaPBh22YvVPyA4hbBAJVU20Rdmps=
 github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=
 golang.org/x/crypto v0.0.0-20210921155107-089bfa567519/go.mod h1:GvvjBRRGRdwPK5ydBHafDWAxML/pGHZbMvKqRZ5+Abc=

heading.go

@@ -12,10 +12,10 @@ type Heading struct {
 }
 
 // NewHeading creates a new section heading. The level can be from 0 to 2.
-func NewHeading (level int, text string) *Label {
+func NewHeading (level int, text string) *Heading {
 	if level < 0 { level = 0 }
 	if level > 2 { level = 2 }
-	this := &Label { TextBox: tomo.NewTextBox() }
+	this := &Heading { TextBox: tomo.NewTextBox() }
 	theme.Apply(this, theme.R("objects", "Heading", fmt.Sprint(level)))
 	this.SetText(text)
 	return this

icon.go

@@ -0,0 +1,42 @@
+package objects
+
+import "image"
+import "git.tebibyte.media/tomo/tomo"
+import "git.tebibyte.media/tomo/tomo/data"
+import "git.tebibyte.media/tomo/tomo/theme"
+import "git.tebibyte.media/tomo/tomo/canvas"
+
+// Icon displays a single icon.
+type Icon struct {
+	tomo.Box
+}
+
+// NewIcon creates a new icon from an icon ID.
+func NewIcon (id theme.Icon, size theme.IconSize) *Icon {
+	this := &Icon {
+		Box: tomo.NewBox(),
+	}
+	theme.Apply(this, theme.R("objects", "Icon", size.String()))
+	this.SetTexture(id.Texture(size))
+	return this
+}
+
+// NewMimeIcon creates a new icon from a MIME type.
+func NewMimeIcon (mime data.Mime, size theme.IconSize) *Icon {
+	this := &Icon {
+		Box: tomo.NewBox(),
+	}
+	theme.Apply(this, theme.R("objects", "Icon", size.String()))
+	this.SetTexture(theme.MimeIcon(mime, size))
+	return this
+}
+
+func (this *Icon) SetTexture (texture canvas.Texture) {
+	this.Box.SetTexture(texture)
+	if texture == nil {
+		this.SetMinimumSize(image.Pt(0, 0))
+	} else {
+		bounds := texture.Bounds()
+		this.SetMinimumSize(bounds.Max.Sub(bounds.Min))
+	}
+}

input.go

@@ -1,5 +1,6 @@
 package objects
 
+import "image"
 import "git.tebibyte.media/tomo/tomo"
 import "git.tebibyte.media/tomo/tomo/text"
 import "git.tebibyte.media/tomo/tomo/theme"
@@ -12,6 +13,7 @@ type TextInput struct {
 	text []rune
 	on struct {
 		enter event.FuncBroadcaster
+		edit  event.FuncBroadcaster
 	}
 }
 
@@ -19,10 +21,13 @@ type TextInput struct {
 func NewTextInput (text string) *TextInput {
 	this := &TextInput { TextBox: tomo.NewTextBox() }
 	theme.Apply(this, theme.R("objects", "TextInput", ""))
+	this.SetAlign(tomo.AlignStart, tomo.AlignMiddle)
 	this.SetText(text)
 	this.SetFocusable(true)
 	this.SetSelectable(true)
+	this.SetOverflow(true, false)
 	this.OnKeyDown(this.handleKeyDown)
+	this.OnScroll(this.handleScroll)
 	return this
 }
 
@@ -43,6 +48,11 @@ func (this *TextInput) OnEnter (callback func ()) event.Cookie {
 	return this.on.enter.Connect(callback)
 }
 
+// OnEdit specifies a function to be called when the user edits the input text.
+func (this *TextInput) OnEdit (callback func ()) event.Cookie {
+	return this.on.edit.Connect(callback)
+}
+
 func (this *TextInput) handleKeyDown (key input.Key, numpad bool) {
 	dot       := this.Dot()
 	modifiers := this.Modifiers()
@@ -50,6 +60,9 @@ func (this *TextInput) handleKeyDown (key input.Key, numpad bool) {
 	sel       := modifiers.Shift
 	changed   := false
 
+	// TODO all this (except editing stuff) really should be moved into the
+	// backend
+
 	switch {
 	case key == input.KeyEnter:
 		this.on.enter.Broadcast()
@@ -86,5 +99,12 @@ func (this *TextInput) handleKeyDown (key input.Key, numpad bool) {
 	}
 
 	this.Select(dot)
-	if changed { this.SetText(string(this.text)) }
+	if changed {
+		this.SetText(string(this.text))
+		this.on.edit.Broadcast()
+	}
+}
+
+func (this *TextInput) handleScroll (x, y float64) {
+	this.ScrollTo(this.ContentBounds().Min.Add(image.Pt(int(x), int(y))))
 }

label.go

@@ -15,4 +15,3 @@ func NewLabel (text string) *Label {
 	this.SetText(text)
 	return this
 }
-

labelcheckbox.go

@@ -0,0 +1,62 @@
+package objects
+
+import "git.tebibyte.media/tomo/tomo"
+import "git.tebibyte.media/tomo/tomo/theme"
+import "git.tebibyte.media/tomo/tomo/input"
+import "git.tebibyte.media/tomo/tomo/event"
+import "git.tebibyte.media/tomo/objects/layouts"
+
+// LabelCheckbox is a checkbox with a label.
+type LabelCheckbox struct {
+	tomo.ContainerBox
+	checkbox *Checkbox
+	label    *Label
+}
+
+// NewLabelCheckbox creates a new labeled checkbox with the specified value and
+// label text.
+func NewLabelCheckbox (value bool, text string) *LabelCheckbox {
+	box := &LabelCheckbox {
+		ContainerBox: tomo.NewContainerBox(),
+		checkbox:     NewCheckbox(value),
+		label:        NewLabel(text),
+	}
+	theme.Apply(box, theme.R("objects", "LabelCheckbox", ""))
+	box.label.SetAlign(tomo.AlignStart, tomo.AlignMiddle)
+	box.Add(box.checkbox)
+	box.Add(box.label)
+	box.SetLayout(layouts.NewGrid([]bool { false, true }, []bool { false }))
+
+	box.OnMouseUp(box.handleMouseUp)
+	box.label.OnMouseUp(box.handleMouseUp)
+	return box
+}
+
+// SetValue sets the value of the checkbox.
+func (this *LabelCheckbox) SetValue (value bool) {
+	this.checkbox.SetValue(value)
+}
+
+// Toggle toggles the value of the checkbox between true and false.
+func (this *LabelCheckbox) Toggle () {
+	this.checkbox.Toggle()
+}
+
+// Value returns the value of the checkbox.
+func (this *LabelCheckbox) Value () bool {
+	return this.checkbox.Value()
+}
+
+// OnValueChange specifies a function to be called when the checkbox's value
+// changes.
+func (this *LabelCheckbox) OnValueChange (callback func ()) event.Cookie {
+	return this.checkbox.OnValueChange(callback)
+}
+
+func (this *LabelCheckbox) handleMouseUp (button input.Button) {
+	if button != input.ButtonLeft { return }
+	if this.MousePosition().In(this.Bounds()) {
+		this.checkbox.SetFocused(true)
+		this.checkbox.Toggle()
+	}
+}

layouts/cut.go

@@ -5,87 +5,46 @@ import "git.tebibyte.media/tomo/tomo"
 
 // Cut is a layout that can be divided into smaller and smaller sections.
 type Cut struct {
-	branches [2]*Cut
-	expand   [2]bool
+	branches []*Cut
+	expand   []bool
 	vertical bool
 }
 
-// Vertical divides the layout in equal halves vertically.
-func (this *Cut) Vertical () (top, bottom *Cut) {
-	this.fill()
-	this.even()
+// NewCut creates and returns a new Cut layout.
+func NewCut () *Cut {
+	return new(Cut)
+}
+
+// Vertical divides the layout vertically. Sections are specified using
+// booleans. If a section is true, it will expand. If false, it will contract.
+func (this *Cut) Vertical (expand ...bool) {
+	this.expand   = expand
 	this.vertical = true
-	return this.Branches()
-}
-
-// Top divides the layout vertically, expanding the top half and contracting the
-// bottom half.
-func (this *Cut) Top () (top, bottom *Cut) {
 	this.fill()
-	this.first()
-	this.vertical = true
-	return this.Branches()
 }
 
-// Bottom divides the layout vertically, expanding the bottom half and
-// contracting the top half.
-func (this *Cut) Bottom () (top, bottom *Cut) {
+// Horizontal divides the layout horizontally. Sections are specified using
+// booleans. If a section is true, it will expand. If false, it will contract.
+func (this *Cut) Horizontal (expand ...bool) {
+	this.expand   = expand
+	this.vertical = false
 	this.fill()
-	this.second()
-	this.vertical = true
-	return this.Branches()
 }
 
-// Horizontal divides the layout in equal halves horizontally.
-func (this *Cut) Horizontal () (top, bottom *Cut) {
-	this.fill()
-	this.even()
-	return this.Branches()
-}
-
-// Left divides the layout horizontally, expanding the left half and contracting
-// the right half.
-func (this *Cut) Left () (top, bottom *Cut) {
-	this.fill()
-	this.first()
-	return this.Branches()
-}
-
-// Right divides the layout horizontally, expanding the right half and
-// contracting the left half.
-func (this *Cut) Right () (top, bottom *Cut) {
-	this.fill()
-	this.second()
-	return this.Branches()
-}
-
-// Branches returns the two halves of this layout.
-func (this *Cut) Branches () (first, second *Cut) {
-	return this.branches[0], this.branches[1]
+// At returns the section of this layout at the specified index.
+func (this *Cut) At (index int) *Cut {
+	return this.branches[index]
 }
 
 func (this *Cut) real () bool {
-	return this != nil && this.branches[0] != nil && this.branches[1] != nil
+	return this != nil && this.branches != nil
 }
 
 func (this *Cut) fill () {
-	this.branches[0] = &Cut { }
-	this.branches[1] = &Cut { }
-}
-
-func (this *Cut) first () {
-	this.expand[0] = true
-	this.expand[1] = false
-}
-
-func (this *Cut) second () {
-	this.expand[0] = false
-	this.expand[1] = true
-}
-
-func (this *Cut) even () {
-	this.expand[0] = true
-	this.expand[1] = true
+	this.branches = make([]*Cut, len(this.expand))
+	for index := range this.branches {
+		this.branches[index] = new(Cut)
+	}
 }
 
 func (this *Cut) MinimumSize (hints tomo.LayoutHints, boxes []tomo.Box) image.Point {
@@ -126,9 +85,11 @@ func (this *Cut) minimumSize (hints tomo.LayoutHints, boxes []tomo.Box) (image.P
 }
 
 func (this *Cut) arrange (hints tomo.LayoutHints, boxes []tomo.Box) []tomo.Box {
+	nChildren := len(this.branches)
+
 	// collect minimum sizes and physical endpoints
-	var minimums [2]image.Point
-	var leaves   [2]tomo.Box
+	var minimums = make([]image.Point,  nChildren)
+	var leaves   = make([]tomo.Box,     nChildren)
 	var nBranches int
 	remaining := boxes
 	for index, branch := range this.branches {
@@ -163,7 +124,7 @@ func (this *Cut) arrange (hints tomo.LayoutHints, boxes []tomo.Box) []tomo.Box {
 	expandingSize := freeSpace / nExpanding
 
 	// calculate the size and position of branches
-	var bounds [2]image.Rectangle
+	var bounds = make([]image.Rectangle, nChildren)
 	x := float64(hints.Bounds.Min.X)
 	y := float64(hints.Bounds.Min.Y)
 	for index, minimum := range minimums {

layouts/flow.go

@@ -0,0 +1,123 @@
+package layouts
+
+import "image"
+import "git.tebibyte.media/tomo/tomo"
+
+// Flow is a grid layout where the number of rows and columns changes depending
+// on the size of the container. It is designed to be used with an overflowing
+// container. If the container does not overflow in the correct direction, the
+// layout will behave like Contract.
+type Flow bool
+
+// FlowVertical is a vertical flow layout.
+const FlowVertical Flow = true
+
+// FlowHorizontal is a horizontal flow layout.
+const FlowHorizontal Flow = false
+
+func (flow Flow) MinimumSize (hints tomo.LayoutHints, boxes []tomo.Box) image.Point {
+	// TODO: write down somewhere that layout minimums aren't taken into
+	// account when the respective direction is overflowed
+	return flow.fallback().MinimumSize(hints, boxes)
+}
+
+func (flow Flow) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
+	if flow.v() && !hints.OverflowY || flow.h() && !hints.OverflowX {
+		flow.fallback().Arrange(hints, boxes)
+	}
+
+	// find a minor size value that will fit all boxes
+	minorSize := 0
+	for _, box := range boxes {
+		boxSize := flow.minor(box.MinimumSize())
+		if boxSize > minorSize { minorSize = boxSize }
+	}
+	if minorSize == 0 { return }
+	minorSteps :=
+		(flow.deltaMinor(hints.Bounds) + flow.minor(hints.Gap)) /
+		(minorSize + flow.minor(hints.Gap))
+
+	// arrange
+	point := hints.Bounds.Min
+	index := 0
+	for index < len(boxes) {
+		// get a slice of boxes for this major step
+		stepIndexEnd := index + minorSteps
+		if stepIndexEnd > len(boxes) { stepIndexEnd = len(boxes) }
+		step := boxes[index:stepIndexEnd]
+		index += minorSteps
+		
+		// find a major size that will fit all boxes on this major step
+		majorSize := 0
+		for _, box := range step {
+			boxSize := flow.major(box.MinimumSize())
+			if boxSize > majorSize { majorSize = boxSize }
+		}
+		if majorSize == 0 { continue }
+
+		// arrange all boxes on this major step
+		var size image.Point
+		size = flow.incrMajor(size, majorSize)
+		size = flow.incrMinor(size, minorSize)
+		for _, box := range step {
+			bounds := image.Rectangle { Min: point, Max: point.Add(size) }
+			box.SetBounds(bounds)
+
+			point = flow.incrMinor(point, minorSize + flow.minor(hints.Gap))
+		}
+
+		if flow.v() {
+			point.Y += majorSize + hints.Gap.Y
+			point.X = hints.Bounds.Min.X
+		} else {
+			point.X += majorSize + hints.Gap.X
+			point.Y = hints.Bounds.Min.Y
+		}
+	}
+}
+
+func (flow Flow) v () bool { return flow == FlowVertical   }
+func (flow Flow) h () bool { return flow == FlowHorizontal }
+
+func (flow Flow) minor (point image.Point) int {
+	if flow.v() {
+		return point.X
+	} else {
+		return point.Y
+	}
+}
+func (flow Flow) major (point image.Point) int {
+	if flow.v() {
+		return point.Y
+	} else {
+		return point.X
+	}
+}
+func (flow Flow) incrMinor (point image.Point, delta int) image.Point {
+	if flow.v() {
+		point.X += delta
+		return point
+	} else {
+		point.Y += delta
+		return point
+	}
+}
+func (flow Flow) incrMajor (point image.Point, delta int) image.Point {
+	if flow.v() {
+		point.Y += delta
+		return point
+	} else {
+		point.X += delta
+		return point
+	}
+}
+func (flow Flow) deltaMinor (rectangle image.Rectangle) int {
+	if flow.v() {
+		return rectangle.Dx()
+	} else {
+		return rectangle.Dy()
+	}
+}
+func (flow Flow) fallback () tomo.Layout {
+	return Contract(flow)
+}

layouts/grid.go

@@ -0,0 +1,108 @@
+package layouts
+
+import "math"
+import "image"
+import "git.tebibyte.media/tomo/tomo"
+
+// Grid is a layout that arranges boxes in a grid formation with distinct rows
+// and columns. It is great for creating forms.
+type Grid struct {
+	xExpand []bool
+	yExpand []bool
+}
+
+// NewGrid creates a new grid layout. Rows and columns are specified as slices
+// of booleans, where true means a row or column will expand and false means it
+// will contract. Boxes are laid out left to right, then top to bottom. Boxes
+// that go beyond the lengh of rows will be laid out according to columns, but
+// they will not expand vertically.
+func NewGrid (columns, rows []bool) *Grid {
+	this := &Grid {
+		xExpand: columns,
+		yExpand: rows,
+	}
+	return this
+}
+
+func (this *Grid) MinimumSize (hints tomo.LayoutHints, boxes []tomo.Box) image.Point {
+	cols, rows := this.minimums(boxes)
+	size := image.Pt (
+		(len(cols) - 1) * hints.Gap.X,
+		(len(rows) - 1) * hints.Gap.Y)
+	for _, width  := range cols { size.X += width  }
+	for _, height := range rows { size.Y += height }
+	return size
+}
+
+func (this *Grid) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
+	xExpand := func (index int) bool {
+		return this.xExpand[index]
+	}
+	yExpand := func (index int) bool {
+		if index < len(this.yExpand) { return this.yExpand[index] }
+		return false
+	}
+
+	cols, rows := this.minimums(boxes)
+	expand(hints, cols, hints.Bounds.Dx(), xExpand)
+	expand(hints, rows, hints.Bounds.Dy(), yExpand)
+
+	position := hints.Bounds.Min
+	for index, box := range boxes {
+		col, row := index % len(cols), index / len(cols)
+		box.SetBounds(image.Rectangle {
+			Min: position,
+			Max: position.Add(image.Pt(cols[col], rows[row])),
+		})
+		if col == len(cols) - 1 {
+			position.X = hints.Bounds.Min.X
+			position.Y += rows[row] + hints.Gap.Y
+		} else {
+			position.X += cols[col] + hints.Gap.X
+		}
+	}
+}
+
+func (this *Grid) minimums (boxes []tomo.Box) ([]int, []int) {
+	nCols, nRows := this.dimensions(boxes)
+	cols,  rows  := make([]int, nCols), make([]int, nRows)
+
+	for index, box := range boxes {
+		col, row := index % len(cols), index / len(cols)
+		minimum := box.MinimumSize()
+		if cols[col] < minimum.X {
+			cols[col] = minimum.X
+		}
+		if rows[row] < minimum.Y {
+			rows[row] = minimum.Y
+		}
+	}
+	
+	return cols, rows
+}
+
+func (this *Grid) dimensions (boxes []tomo.Box) (int, int) {
+	return len(this.xExpand), ceilDiv(len(boxes), len(this.xExpand)) 
+}
+
+func expand (hints tomo.LayoutHints, sizes []int, space int, expands func (int) bool) {
+	gaps       := len(sizes) - 1
+	freeSpace  := float64(space - hints.Gap.Y * gaps)
+	nExpanding := 0; for index, minimum := range sizes {
+		if expands(index) {
+			nExpanding ++
+		} else {
+			freeSpace -= float64(minimum)
+		}
+	}
+	expandingSize := freeSpace / float64(nExpanding)
+	for index := range sizes {
+		if expands(index) {
+			sizes[index] = int(expandingSize)
+		}
+	}
+}
+
+func ceilDiv (x, y int) int {
+	return int(math.Ceil(float64(x) / float64(y)))
+}

layouts/layouts.go

@@ -3,86 +3,93 @@ package layouts
 import "image"
 import "git.tebibyte.media/tomo/tomo"
 
-type Row struct { }
+// Contract is a layout that arranges boxes in a simple row or column according
+// to their minimum sizes.
+type Contract bool
 
-func (Row) MinimumSize (hints tomo.LayoutHints, boxes []tomo.Box) image.Point {
-	dot := image.Point { }
-	for _, box := range boxes {
-		minimum := box.MinimumSize()
-		dot.X += minimum.X
-		if dot.Y < minimum.Y {
-			dot.Y = minimum.Y
+// ContractVertical is a vertical contracted layout.
+const ContractVertical Contract = true
+
+// ContractHorizontal is a horizontal contracted layout.
+const ContractHorizontal Contract = false
+
+func (contract Contract) MinimumSize (hints tomo.LayoutHints, boxes []tomo.Box) image.Point {
+	if contract.v() {
+		dot := image.Point { }
+		for _, box := range boxes {
+			minimum := box.MinimumSize()
+			dot.Y += minimum.Y
+			if dot.X < minimum.X {
+				dot.X = minimum.X
+			}
+		}
+		dot.Y += hints.Gap.Y * (len(boxes) - 1)
+		return dot
+	} else {
+		dot := image.Point { }
+		for _, box := range boxes {
+			minimum := box.MinimumSize()
+			dot.X += minimum.X
+			if dot.Y < minimum.Y {
+				dot.Y = minimum.Y
+			}
+		}
+		dot.X += hints.Gap.X * (len(boxes) - 1)
+		return dot
+	}
+}
+
+func (contract Contract) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
+	if contract.v() {
+		dot := hints.Bounds.Min
+		for index, box := range boxes {
+			if index > 0 { dot.Y += hints.Gap.Y }
+			minimum := box.MinimumSize()
+			box.SetBounds(image.Rectangle {
+				Min: dot,
+				Max: dot.Add(image.Pt(hints.Bounds.Dx(), minimum.Y)),
+			})
+			dot.Y += minimum.Y
+		}
+		
+		height := dot.Y - hints.Bounds.Min.Y
+		offset := 0
+		
+		switch hints.AlignY {
+		case tomo.AlignMiddle:
+			offset = (hints.Bounds.Dy() - height) / 2
+		case tomo.AlignEnd:
+			offset = hints.Bounds.Dy() - height
+		}
+		for _, box := range boxes {
+			box.SetBounds(box.Bounds().Add(image.Pt(0, offset)))
+		}
+	} else {
+		dot := hints.Bounds.Min
+		for index, box := range boxes {
+			if index > 0 { dot.X += hints.Gap.X }
+			minimum := box.MinimumSize()
+			box.SetBounds(image.Rectangle {
+				Min: dot,
+				Max: dot.Add(image.Pt(minimum.X, hints.Bounds.Dy())),
+			})
+			dot.X += minimum.X
+		}
+
+		width  := dot.X - hints.Bounds.Min.X
+		offset := 0
+		
+		switch hints.AlignX {
+		case tomo.AlignMiddle:
+			offset = (hints.Bounds.Dx() - width) / 2
+		case tomo.AlignEnd:
+			offset = hints.Bounds.Dx() - width
+		}
+		for _, box := range boxes {
+			box.SetBounds(box.Bounds().Add(image.Pt(offset, 0)))
 		}
 	}
-	dot.X += hints.Gap.X * (len(boxes) - 1)
-	return dot
 }
 
-func (Row) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
-	// TODO respect alignment value
-	dot := hints.Bounds.Min
-	for index, box := range boxes {
-		if index > 0 { dot.X += hints.Gap.X }
-		minimum := box.MinimumSize()
-		box.SetBounds(image.Rectangle {
-			Min: dot,
-			Max: dot.Add(image.Pt(minimum.X, hints.Bounds.Dy())),
-		})
-		dot.X += minimum.X
-	}
-
-	width  := dot.X - hints.Bounds.Min.X
-	offset := 0
-	
-	switch hints.AlignX {
-	case tomo.AlignMiddle:
-		offset = (hints.Bounds.Dx() - width) / 2
-	case tomo.AlignEnd:
-		offset = hints.Bounds.Dx() - width
-	}
-	for _, box := range boxes {
-		box.SetBounds(box.Bounds().Add(image.Pt(offset, 0)))
-	}
-}
-
-type Column struct { }
-
-func (Column) MinimumSize (hints tomo.LayoutHints, boxes []tomo.Box) image.Point {
-	dot := image.Point { }
-	for _, box := range boxes {
-		minimum := box.MinimumSize()
-		dot.Y += minimum.Y
-		if dot.X < minimum.X {
-			dot.X = minimum.X
-		}
-	}
-	dot.Y += hints.Gap.Y * (len(boxes) - 1)
-	return dot
-}
-
-func (Column) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
-	// TODO respect alignment value
-	dot := hints.Bounds.Min
-	for index, box := range boxes {
-		if index > 0 { dot.Y += hints.Gap.Y }
-		minimum := box.MinimumSize()
-		box.SetBounds(image.Rectangle {
-			Min: dot,
-			Max: dot.Add(image.Pt(hints.Bounds.Dx(), minimum.Y)),
-		})
-		dot.Y += minimum.Y
-	}
-	
-	height := dot.Y - hints.Bounds.Min.Y
-	offset := 0
-	
-	switch hints.AlignY {
-	case tomo.AlignMiddle:
-		offset = (hints.Bounds.Dy() - height) / 2
-	case tomo.AlignEnd:
-		offset = hints.Bounds.Dy() - height
-	}
-	for _, box := range boxes {
-		box.SetBounds(box.Bounds().Add(image.Pt(0, offset)))
-	}
-}
+func (contract Contract) v () bool { return contract == ContractVertical   }
+func (contract Contract) h () bool { return contract == ContractHorizontal }

numberinput.go

@@ -0,0 +1,100 @@
+package objects
+
+import "math"
+import "strconv"
+import "git.tebibyte.media/tomo/tomo"
+import "git.tebibyte.media/tomo/tomo/theme"
+import "git.tebibyte.media/tomo/tomo/input"
+import "git.tebibyte.media/tomo/tomo/event"
+import "git.tebibyte.media/tomo/objects/layouts"
+
+// NumberInput is an editable text box which accepts only numbers, and has
+// controls to increment and decrement its value.
+type NumberInput struct {
+	tomo.ContainerBox
+	input     *TextInput
+	increment *Button
+	decrement *Button
+	on struct {
+		enter event.FuncBroadcaster
+		edit  event.FuncBroadcaster
+	}
+}
+
+// NewNumberInput creates a new number input with the specified value.
+func NewNumberInput (value float64) *NumberInput {
+	box := &NumberInput {
+		ContainerBox: tomo.NewContainerBox(),
+		input:        NewTextInput(""),
+		increment:    NewButton(""),
+		decrement:    NewButton(""),
+	}
+	theme.Apply(box, theme.R("objects", "NumberInput", ""))
+	box.Add(box.input)
+	box.Add(box.decrement)
+	box.Add(box.increment)
+	box.SetLayout(layouts.NewGrid([]bool { true, false, false }, []bool { true }))
+	box.increment.SetIcon(theme.IconActionIncrement)
+	box.decrement.SetIcon(theme.IconActionDecrement)
+	
+	box.SetValue(value)
+	
+	box.CaptureScroll(true)
+	box.CaptureKeyboard(true)
+	
+	box.OnScroll(box.handleScroll)
+	box.OnKeyDown(box.handleKeyDown)
+	box.input.OnEnter(box.handleEnter)
+	box.input.OnEdit(box.on.edit.Broadcast)
+	box.increment.OnClick(func () { box.shift(1)  })
+	box.decrement.OnClick(func () { box.shift(-1) })
+	return box
+}
+
+// SetValue sets the value of the input.
+func (this *NumberInput) SetValue (value float64) {
+	this.input.SetText(strconv.FormatFloat(value, 'g', -1, 64))
+}
+
+// Value returns the value of the input.
+func (this *NumberInput) Value () float64 {
+	value, _ := strconv.ParseFloat(this.input.Text(), 64)
+	return value
+}
+
+// OnEnter specifies a function to be called when the user presses enter within
+// the text input.
+func (this *NumberInput) OnEnter (callback func ()) event.Cookie {
+	return this.on.enter.Connect(callback)
+}
+
+// OnEdit specifies a function to be called when the user edits the input value.
+func (this *NumberInput) OnEdit (callback func ()) event.Cookie {
+	return this.on.edit.Connect(callback)
+}
+
+func (this *NumberInput) shift (by int) {
+	this.SetValue(this.Value() + float64(by))
+	this.on.edit.Broadcast()
+}
+
+func (this *NumberInput) handleKeyDown (key input.Key, numpad bool) {
+	switch key {
+	case input.KeyUp:   this.shift(1)
+	case input.KeyDown: this.shift(-1)
+	default:            this.input.handleKeyDown(key, numpad)
+	}
+}
+
+func (this *NumberInput) handleScroll (x, y float64) {
+	if x == 0 {
+		this.shift(-int(math.Round(y)))
+	} else {
+		this.input.handleScroll(x, y)
+	}
+}
+
+func (this *NumberInput) handleEnter () {
+	this.SetValue(this.Value())
+	this.on.enter.Broadcast()
+}

scrollbar.go

@@ -0,0 +1,364 @@
+package objects
+
+import "image"
+import "git.tebibyte.media/tomo/tomo"
+import "git.tebibyte.media/tomo/tomo/theme"
+import "git.tebibyte.media/tomo/tomo/input"
+import "git.tebibyte.media/tomo/tomo/event"
+
+// Scrollbar is a special type of slider that can control the scroll of any
+// overflowing ContainerBox.
+type Scrollbar struct {
+	tomo.ContainerBox
+	handle     *SliderHandle
+	layout     scrollbarLayout
+	dragging   bool
+	dragOffset image.Point
+
+	linkCookie event.Cookie
+
+	on struct {
+		valueChange event.FuncBroadcaster
+	}
+}
+
+func newScrollbar (orient string) *Scrollbar {
+	this := &Scrollbar {
+		ContainerBox: tomo.NewContainerBox(),
+		handle: &SliderHandle {
+			Box: tomo.NewBox(),
+		},
+		layout: scrollbarLayout {
+			vertical: orient == "vertical",
+		},
+	}
+
+	this.Add(this.handle)
+	this.SetFocusable(true)
+
+	this.CaptureDND(true)
+	this.CaptureMouse(true)
+	this.CaptureScroll(true)
+	this.CaptureKeyboard(true)
+
+	this.OnKeyDown(this.handleKeyDown)
+	this.OnMouseDown(this.handleMouseDown)
+	this.OnMouseUp(this.handleMouseUp)
+	this.OnMouseMove(this.handleMouseMove)
+	this.OnScroll(this.handleScroll)
+	theme.Apply(this.handle, theme.R("objects", "SliderHandle", orient))
+	theme.Apply(this,        theme.R("objects", "Slider", orient))
+	return this
+}
+
+// NewVerticalScrollbar creates a new vertical scrollbar.
+func NewVerticalScrollbar () *Scrollbar {
+	return newScrollbar("vertical")
+}
+
+// NewHorizontalScrollbar creates a new horizontal scrollbar.
+func NewHorizontalScrollbar () *Scrollbar {
+	return newScrollbar("horizontal")
+}
+
+// Link assigns this scrollbar to a ContentBox. Closing the returned cookie will
+// unlink it.
+func (this *Scrollbar) Link (box tomo.ContentBox) event.Cookie {
+	this.layout.linked = box
+	this.linkCookie = this.newLinkCookie (
+		box.OnContentBoundsChange(this.handleLinkedContentBoundsChange))
+	this.SetLayout(this.layout)
+	return this.linkCookie
+}
+
+func (this *Scrollbar) handleLinkedContentBoundsChange () {
+	if this.layout.linked == nil { return }
+	previousValue := this.layout.value
+	trackLength := this.layout.contentLength() - this.layout.viewportLength()
+	if trackLength == 0 {
+		this.layout.value = 0
+	} else {
+		this.layout.value = this.layout.contentPos() / trackLength
+	}
+	this.SetLayout(this.layout)
+	if this.layout.value != previousValue {
+		this.on.valueChange.Broadcast()
+	}
+}
+
+// SetValue sets the value of the scrollbar between 0 and 1, where 0 is scrolled
+// all the way to the left/top, and 1 is scrolled all the way to the
+// right/bottom.
+func (this *Scrollbar) SetValue (value float64) {
+	if this.layout.linked == nil { return }
+	if value > 1 { value = 1 }
+	if value < 0 { value = 0 }
+	
+	trackLength := this.layout.contentLength() - this.layout.viewportLength()
+	position    := trackLength * value
+	point       := this.layout.linked.ContentBounds().Min
+	if this.layout.vertical {
+		point.Y = -int(position)
+	} else {
+		point.X = -int(position)
+	}
+	this.layout.linked.ScrollTo(point)
+	
+}
+
+// Value returns the value of the scrollbar between 0 and 1 where 0 is scrolled
+// all the way to the left/top, and 1 is scrolled all the way to the
+// right/bottom.
+func (this *Scrollbar) Value () float64 {
+	if this.layout.linked == nil { return 0 }
+	return this.layout.value
+}
+
+// OnValueChange specifies a function to be called when the position of the
+// scrollbar changes.
+func (this *Scrollbar) OnValueChange (callback func ()) event.Cookie {
+	return this.on.valueChange.Connect(callback)
+}
+
+func (this *Scrollbar) handleKeyDown (key input.Key, numpad bool) {
+	var increment float64; if this.layout.vertical {
+		increment = -0.05
+	} else {
+		increment = 0.05
+	}
+
+	switch key {
+	case input.KeyUp, input.KeyLeft:
+		if this.Modifiers().Alt {
+			this.SetValue(0)
+		} else {
+			this.SetValue(this.Value() - increment)
+		}
+	case input.KeyDown, input.KeyRight:
+		if this.Modifiers().Alt {
+			this.SetValue(1)
+		} else {
+			this.SetValue(this.Value() + increment)
+		}
+	case input.KeyHome:
+		this.SetValue(0)
+	case input.KeyEnd:
+		this.SetValue(1)
+	}
+}
+
+func (this *Scrollbar) handleMouseDown (button input.Button) {
+	pointer := this.MousePosition()
+	handle  := this.handle.Bounds()
+
+	within := pointer.In(handle)
+	var above bool; if this.layout.vertical {
+		above = pointer.Y < handle.Min.Y + handle.Dy() / 2
+	} else {
+		above = pointer.X < handle.Min.X + handle.Dx() / 2
+	}
+
+	switch button {
+	case input.ButtonLeft:
+		if within {
+			this.dragging   = true
+			this.dragOffset =
+				pointer.Sub(this.handle.Bounds().Min).
+				Add(this.InnerBounds().Min)
+			this.drag()
+		} else {
+			this.dragOffset = this.fallbackDragOffset()
+			this.dragging   = true
+			this.drag()
+		}
+	case input.ButtonMiddle:
+		if above {
+			this.scrollBy(this.pageSize())
+		} else {
+			this.scrollBy(-this.pageSize())
+		}
+	case input.ButtonRight:
+		if above {
+			this.scrollBy(this.stepSize())
+		} else {
+			this.scrollBy(-this.stepSize())
+		}
+	}
+}
+
+func (this *Scrollbar) handleMouseUp (button input.Button) {
+	if button != input.ButtonLeft || !this.dragging { return }
+	this.dragging = false
+}
+
+func (this *Scrollbar) handleMouseMove () {
+	if !this.dragging { return }
+	this.drag()
+}
+
+func (this *Scrollbar) handleScroll (x, y float64) {
+	if this.layout.linked == nil { return }
+	this.layout.linked.ScrollTo (
+		this.layout.linked.ContentBounds().Min.
+		Sub(image.Pt(int(x), int(y))))
+}
+
+func (this *Scrollbar) drag () {
+	pointer := this.MousePosition().Sub(this.dragOffset)
+	gutter  := this.InnerBounds()
+	handle  := this.handle.Bounds()
+
+	if this.layout.vertical {
+		this.SetValue (
+			float64(pointer.Y) /
+			float64(gutter.Dy() - handle.Dy()))
+	} else {
+		this.SetValue (
+			float64(pointer.X) /
+			float64(gutter.Dx() - handle.Dx()))
+	}
+}
+
+func (this *Scrollbar) fallbackDragOffset () image.Point {
+	if this.layout.vertical {
+		return this.InnerBounds().Min.
+			Add(image.Pt(0, this.handle.Bounds().Dy() / 2))
+	} else {
+		return this.InnerBounds().Min.
+			Add(image.Pt(this.handle.Bounds().Dx() / 2, 0))
+	}
+}
+
+func (this *Scrollbar) pageSize () int {
+	if this.layout.linked == nil { return 0 }
+	viewport := this.layout.linked.InnerBounds()
+	if this.layout.vertical {
+		return viewport.Dy()
+	} else {
+		return viewport.Dx()
+	}
+}
+
+func (this *Scrollbar) stepSize () int {
+	// FIXME: this should not be hardcoded, need to get base font metrics
+	// from theme somehow. should be (emspace, lineheight)
+	return 16
+}
+
+func (this *Scrollbar) scrollBy (distance int) {
+	if this.layout.linked == nil { return }
+	var vector image.Point; if this.layout.vertical {
+		vector.Y = distance
+	} else {
+		vector.X = distance
+	}
+	this.layout.linked.ScrollTo (
+		this.layout.linked.ContentBounds().Min.
+		Add(vector))
+}
+
+type scrollbarCookie struct {
+	owner *Scrollbar
+	subCookies []event.Cookie
+}
+
+func (this *Scrollbar) newLinkCookie (subCookies ...event.Cookie) *scrollbarCookie {
+	return &scrollbarCookie {
+		owner:      this,
+		subCookies: subCookies,
+	}
+}
+
+func (this *scrollbarCookie) Close () {
+	for _, cookie := range this.subCookies {
+		cookie.Close()
+	}
+	this.owner.layout.linked = nil
+	this.owner.SetLayout(this.owner.layout)
+}
+
+type scrollbarLayout struct {
+	vertical bool
+	value    float64
+	linked   tomo.ContentBox
+}
+
+func (scrollbarLayout) MinimumSize (hints tomo.LayoutHints, boxes []tomo.Box) image.Point {
+	if len(boxes) != 1 { return image.Pt(0, 0) }
+	return boxes[0].MinimumSize()
+}
+
+func (this scrollbarLayout) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
+	if len(boxes) != 1 { return }
+	handle := image.Rectangle { Max: boxes[0].MinimumSize() }
+	gutter := hints.Bounds
+
+	var gutterLength float64;
+	var handleMin    float64;
+	if this.vertical {
+		gutterLength = float64(gutter.Dy())
+		handleMin    = float64(handle.Dy())
+	} else {
+		gutterLength = float64(gutter.Dx())
+		handleMin    = float64(handle.Dx())
+	}
+
+	// calculate handle length
+	handleLength := gutterLength * this.viewportContentRatio()
+	if handleLength < handleMin { handleLength = handleMin }
+	if handleLength >= gutterLength {
+		// just hide the handle if it isn't needed.
+		// TODO: we need a way to hide and show boxes, this is janky as
+		// fuck
+		boxes[0].SetBounds(image.Rect(-16, -16, 0, 0))
+		return
+	}
+	if this.vertical {
+		handle.Max.Y = int(handleLength)
+	} else {
+		handle.Max.X = int(handleLength)
+	}
+
+	// calculate handle position
+	handlePosition := (gutterLength - handleLength) * this.value
+	var handleOffset image.Point
+	if this.vertical {
+		handleOffset = image.Pt(0, int(handlePosition))
+	} else {
+		handleOffset = image.Pt(int(handlePosition), 0)
+	}
+	handle = handle.Sub(handleOffset).Add(gutter.Min)
+	
+	// place handle
+	boxes[0].SetBounds(handle)
+	
+}
+
+func (this scrollbarLayout) viewportContentRatio () float64 {
+	if this.linked == nil { return 0 }
+	return this.viewportLength() / this.contentLength()
+}
+
+func (this scrollbarLayout) viewportLength () float64 {
+	if this.vertical {
+		return float64(this.linked.InnerBounds().Dy())
+	} else {
+		return float64(this.linked.InnerBounds().Dx())
+	}
+}
+
+func (this scrollbarLayout) contentLength () float64 {
+	if this.vertical {
+		return float64(this.linked.ContentBounds().Dy())
+	} else {
+		return float64(this.linked.ContentBounds().Dx())
+	}
+}
+
+func (this scrollbarLayout) contentPos () float64 {
+	if this.vertical {
+		return float64(this.linked.ContentBounds().Min.Y)
+	} else {
+		return float64(this.linked.ContentBounds().Min.X)
+	}
+}

scrollcontainer.go

@@ -0,0 +1,190 @@
+package objects
+
+import "image"
+import "git.tebibyte.media/tomo/tomo"
+import "git.tebibyte.media/tomo/tomo/event"
+import "git.tebibyte.media/tomo/tomo/theme"
+
+// ScrollSide determines which Scrollbars are active in a ScrollContainer.
+type ScrollSide int; const (
+	ScrollVertical ScrollSide = 1 << iota
+	ScrollHorizontal
+	ScrollBoth = ScrollVertical | ScrollHorizontal
+)
+
+// Horizontal returns true if the side includes a horizontal bar.
+func (sides ScrollSide) Horizontal () bool {
+	return sides & ScrollHorizontal > 0
+}
+
+// Vertical returns true if the side includes a vertical bar.
+func (sides ScrollSide) Vertical () bool {
+	return sides & ScrollVertical > 0
+}
+
+// String returns one of:
+//   - both
+//   - horizontal
+//   - vertical
+//   - none
+func (sides ScrollSide) String () string {
+	switch {
+	case sides.Horizontal() && sides.Vertical(): return "both"
+	case sides.Horizontal():                     return "horizontal"
+	case sides.Vertical():                       return "vertical"
+	default:                                     return "none"
+	}
+}
+
+// ScrollContainer couples a ContentBox with one or two Scrollbars.
+type ScrollContainer struct {
+	tomo.ContainerBox
+	layout *scrollContainerLayout
+
+	horizontalCookie event.Cookie
+	verticalCookie   event.Cookie
+}
+
+// NewScrollContainer creates a new scroll container.
+func NewScrollContainer (sides ScrollSide) *ScrollContainer {
+	this := &ScrollContainer {
+		ContainerBox: tomo.NewContainerBox(),
+		layout:       &scrollContainerLayout { },
+	}
+	if sides.Vertical() {
+		this.layout.vertical = NewVerticalScrollbar()
+		this.Add(this.layout.vertical)
+	}
+	if sides.Horizontal() {
+		this.layout.horizontal = NewHorizontalScrollbar()
+		this.Add(this.layout.horizontal)
+	}
+	this.CaptureScroll(true)
+	this.OnScroll(this.handleScroll)
+	theme.Apply(this, theme.R("objects", "ScrollContainer", sides.String()))
+	this.SetLayout(this.layout)
+	return this
+}
+
+// SetRoot sets the root child of the ScrollContainer. There can only be one at
+// a time, and setting it will remove and unlink the current child if there is
+// one.
+func (this *ScrollContainer) SetRoot (root tomo.ContentBox) {
+	if this.layout.root != nil {
+		// delete root and close cookies
+		this.Delete(this.layout.root)
+		if this.horizontalCookie != nil {
+			this.horizontalCookie.Close()
+			this.horizontalCookie = nil
+		}
+		if this.verticalCookie != nil {
+			this.verticalCookie.Close()
+			this.verticalCookie = nil
+		}
+	}
+	this.layout.root = root
+	if root != nil {
+		// insert root at the beginning (for keynav)
+		switch {
+		case this.layout.vertical != nil:
+			this.Insert(root, this.layout.vertical)
+		case this.layout.horizontal != nil:
+			this.Insert(root, this.layout.horizontal)
+		default:
+			this.Add(root)
+		}
+		
+		// link root and remember cookies
+		if this.layout.horizontal != nil {
+			this.horizontalCookie = this.layout.horizontal.Link(root)
+		}
+		if this.layout.vertical != nil {
+			this.verticalCookie =  this.layout.vertical.Link(root)
+		}
+	}
+}
+
+// SetValue sets the horizontal and vertical scrollbar values where 0 is all the
+// way to the left/top, and 1 is all the way to the right/bottom.
+func (this *ScrollContainer) SetValue (x, y float64) {
+	if this.layout.horizontal != nil {
+		this.layout.horizontal.SetValue(x)
+	}
+	if this.layout.vertical != nil {
+		this.layout.vertical.SetValue(y)
+	}
+}
+
+// Value returns the horizontal and vertical scrollbar values where 0 is all the
+// way to the left/top, and 1 is all the way to the right/bottom.
+func (this *ScrollContainer) Value () (x, y float64) {
+	if this.layout.horizontal != nil {
+		x = this.layout.horizontal.Value()
+	}
+	if this.layout.vertical != nil {
+		y = this.layout.vertical.Value()
+	}
+	return x, y
+}
+
+func (this *ScrollContainer) handleScroll (x, y float64) {
+	if this.layout.root == nil { return }
+	this.layout.root.ScrollTo (
+		this.layout.root.ContentBounds().Min.
+		Sub(image.Pt(int(x), int(y))))
+}
+
+type scrollContainerLayout struct {
+	root       tomo.ContentBox
+	horizontal *Scrollbar
+	vertical   *Scrollbar
+}
+
+func (this *scrollContainerLayout) MinimumSize (hints tomo.LayoutHints, boxes []tomo.Box) image.Point {
+	var minimum image.Point; if this.root != nil {
+		minimum = this.root.MinimumSize()
+	}
+	if this.horizontal != nil {
+		minimum.Y += this.horizontal.MinimumSize().Y
+	}
+	if this.vertical != nil {
+		minimum.X += this.vertical.MinimumSize().X
+		minimum.Y = max(minimum.Y, this.vertical.MinimumSize().Y)
+	}
+	if this.horizontal != nil {
+		minimum.X = max(minimum.X, this.horizontal.MinimumSize().X)
+	}
+	return minimum
+}
+
+func (this *scrollContainerLayout) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
+	rootBounds := hints.Bounds
+	if this.horizontal != nil {
+		rootBounds.Max.Y -= this.horizontal.MinimumSize().Y
+	}
+	if this.vertical != nil {
+		rootBounds.Max.X -= this.vertical.MinimumSize().X
+	}
+	if this.root != nil {
+		this.root.SetBounds(rootBounds)
+	}
+	if this.horizontal != nil {
+		this.horizontal.SetBounds(image.Rect (
+			hints.Bounds.Min.X,
+			rootBounds.Max.Y,
+			rootBounds.Max.X,
+			hints.Bounds.Max.Y))
+	}
+	if this.vertical != nil {
+		this.vertical.SetBounds(image.Rect (
+			rootBounds.Max.X,
+			hints.Bounds.Min.Y,
+			hints.Bounds.Max.X,
+			rootBounds.Max.Y))
+	}
+}
+
+func max (x, y int) int {
+	if x > y { return x }
+	return y
+}

separator.go

@@ -16,4 +16,3 @@ func NewSeparator () *Separator {
 	theme.Apply(this, theme.R("objects", "Separator", ""))
 	return this
 }
-

slider.go

@@ -6,20 +6,22 @@ import "git.tebibyte.media/tomo/tomo/theme"
 import "git.tebibyte.media/tomo/tomo/input"
 import "git.tebibyte.media/tomo/tomo/event"
 
-// UNDER CONSTRUCTION!
-
+// Slider is a control that selects a numeric value between 0 and 1.
 type Slider struct {
 	tomo.ContainerBox
 	handle     *SliderHandle
 	layout     sliderLayout
 	dragging   bool
 	dragOffset image.Point
+	step       float64
 
 	on struct {
-		valueChange event.FuncBroadcaster
+		slide event.FuncBroadcaster
 	}
 }
 
+// SliderHandle is a simple object that serves as a handle for sliders and
+// scrollbars. It is completely inert.
 type SliderHandle struct {
 	tomo.Box
 }
@@ -33,78 +35,98 @@ func newSlider (orient string, value float64) *Slider {
 		layout: sliderLayout {
 			vertical: orient == "vertical",
 		},
+		step: 0.05,
 	}
 
 	this.Add(this.handle)
 	this.SetFocusable(true)
-	this.SetPropagateEvents(false)
+
+	this.CaptureDND(true)
+	this.CaptureMouse(true)
+	this.CaptureScroll(true)
+	this.CaptureKeyboard(true)
+
 	this.SetValue(value)
 	this.OnKeyDown(this.handleKeyDown)
 	this.OnMouseDown(this.handleMouseDown)
 	this.OnMouseUp(this.handleMouseUp)
 	this.OnMouseMove(this.handleMouseMove)
+	this.OnScroll(this.handleScroll)
 	theme.Apply(this.handle, theme.R("objects", "SliderHandle", orient))
 	theme.Apply(this,        theme.R("objects", "Slider", orient))
 	return this
 }
 
+// NewVerticalSlider creates a new vertical slider with the specified value.
 func NewVerticalSlider (value float64) *Slider {
 	return newSlider("vertical", value)
 }
 
+// NewHorizontalSlider creates a new horizontal slider with the specified value.
 func NewHorizontalSlider (value float64) *Slider {
 	return newSlider("horizontal", value)
 }
 
+// SetValue sets the value of the slider between 0 and 1.
 func (this *Slider) SetValue (value float64) {
 	if value < 0 { value = 0 }
 	if value > 1 { value = 1 }
 	if value == this.layout.value { return }
 	this.layout.value = value
 	this.SetLayout(this.layout)
-	this.on.valueChange.Broadcast()
 }
 
+// Value returns the value of the slider between 0 and 1.
 func (this *Slider) Value () float64 {
 	return this.layout.value
 }
 
-func (this *Slider) OnValueChange (callback func ()) event.Cookie {
-	return this.on.valueChange.Connect(callback)
+// OnValueChange specifies a function to be called when the user moves the
+// slider.
+func (this *Slider) OnSlide (callback func ()) event.Cookie {
+	return this.on.slide.Connect(callback)
 }
 
 func (this *Slider) handleKeyDown (key input.Key, numpad bool) {
+	var increment float64; if this.layout.vertical {
+		increment = -0.05
+	} else {
+		increment = 0.05
+	}
+
 	switch key {
 	case input.KeyUp, input.KeyLeft:
 		if this.Modifiers().Alt {
 			this.SetValue(0)
 		} else {
-			this.SetValue(this.Value() - 0.05)		
+			this.SetValue(this.Value() - increment)
 		}
+		this.on.slide.Broadcast()
 	case input.KeyDown, input.KeyRight:
 		if this.Modifiers().Alt {
 			this.SetValue(1)
 		} else {
-			this.SetValue(this.Value() + 0.05)		
+			this.SetValue(this.Value() + increment)
 		}
+		this.on.slide.Broadcast()
 	case input.KeyHome:
 		this.SetValue(0)
+		this.on.slide.Broadcast()
 	case input.KeyEnd:
 		this.SetValue(1)
+		this.on.slide.Broadcast()
 	}
 }
 
 func (this *Slider) handleMouseDown (button input.Button) {
 	pointer := this.MousePosition()
 	handle  := this.handle.Bounds()
-	var above, within bool
 	
-	if pointer.In(handle) {
-		within = true
-	} else if this.layout.vertical {
-		above = pointer.Y < handle.Min.Y
+	within := pointer.In(handle)
+	var above bool; if this.layout.vertical {
+		above = pointer.Y < handle.Min.Y + handle.Dy() / 2
 	} else {
-		above = pointer.X < handle.Min.X
+		above = pointer.X < handle.Min.X + handle.Dx() / 2
 	}
 
 	switch button {
@@ -123,14 +145,18 @@ func (this *Slider) handleMouseDown (button input.Button) {
 	case input.ButtonMiddle:
 		if above {
 			this.SetValue(0)
+			this.on.slide.Broadcast()
 		} else {
 			this.SetValue(1)
+			this.on.slide.Broadcast()
 		}
 	case input.ButtonRight:
 		if above {
-			this.SetValue(this.Value() - 0.05)
+			this.SetValue(this.Value() - this.step)
+			this.on.slide.Broadcast()
 		} else {
-			this.SetValue(this.Value() + 0.05)
+			this.SetValue(this.Value() + this.step)
+			this.on.slide.Broadcast()
 		}
 	}
 }
@@ -145,6 +171,12 @@ func (this *Slider) handleMouseMove () {
 	this.drag()
 }
 
+func (this *Slider) handleScroll (x, y float64) {
+	delta := (x + y) * 0.005
+	this.SetValue(this.Value() + delta)
+	this.on.slide.Broadcast()
+}
+
 func (this *Slider) drag () {
 	pointer := this.MousePosition().Sub(this.dragOffset)
 	gutter  := this.InnerBounds()
@@ -152,6 +184,7 @@ func (this *Slider) drag () {
 
 	if this.layout.vertical {
 		this.SetValue (
+			1 -
 			float64(pointer.Y) /
 			float64(gutter.Dy() - handle.Dy()))
 	} else {
@@ -159,6 +192,7 @@ func (this *Slider) drag () {
 			float64(pointer.X) /
 			float64(gutter.Dx() - handle.Dx()))
 	}
+	this.on.slide.Broadcast()
 }
 
 func (this *Slider) fallbackDragOffset () image.Point {
@@ -188,8 +222,8 @@ func (this sliderLayout) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
 
 	if this.vertical {
 		height := gutter.Dy() - handle.Dy()
-		offset := int(float64(height) * this.value)
-		gutter.Max.X = handle.Max.X
+		offset := int(float64(height) * (1 - this.value))
+		handle.Max.X = gutter.Dx()
 		boxes[0].SetBounds (
 			handle.
 			Add(image.Pt(0, offset)).
@@ -197,7 +231,7 @@ func (this sliderLayout) Arrange (hints tomo.LayoutHints, boxes []tomo.Box) {
 	} else {
 		width  := gutter.Dx() - handle.Dx()
 		offset := int(float64(width) * this.value)
-		gutter.Max.Y = handle.Max.Y
+		handle.Max.Y = gutter.Dy()
 		boxes[0].SetBounds (
 			handle.
 			Add(image.Pt(offset, 0)).

textview.go

@@ -0,0 +1,27 @@
+package objects
+
+import "image"
+import "git.tebibyte.media/tomo/tomo"
+import "git.tebibyte.media/tomo/tomo/theme"
+
+// TextView is an area for displaying a large amount of multi-line text.
+type TextView struct {
+	tomo.TextBox
+}
+
+// NewTextView creates a new text view.
+func NewTextView (text string) *TextView {
+	this := &TextView { TextBox: tomo.NewTextBox() }
+	theme.Apply(this, theme.R("objects", "TextView", ""))
+	this.SetFocusable(true)
+	this.SetSelectable(true)
+	this.SetText(text)
+	this.SetOverflow(false, true)
+	this.SetWrap(true)
+	this.OnScroll(this.handleScroll)
+	return this
+}
+
+func (this *TextView) handleScroll (x, y float64) {
+	this.ScrollTo(this.ContentBounds().Min.Add(image.Pt(int(x), int(y))))
+}